Investigation into the effect of lateral and longitudinal loads on railroad spike stress magnitude and location using finite element analysis

Multiple wide-gage derailments have recently been attributed to broken spikes in track constructed with premium elastic fastening systems. Premium fasteners on timber crossties were introduced into heavy axle load (HAL) freight service in North America over the past few decades and have gained popularity given they are thought to reduce maintenance costs, reduce rail-rollover risk, and they do not generally require rail anchors. However, given recent derailments and identification of failed spikes during field testing at higher rates than traditional fasteners, the University of Illinois at Urbana-Champaign is investigating the stress state of cut spikes in premium fasteners. This paper provides background on the broken spike problem and initial results from a validated finite element model that was developed to quantify the magnitude and location of spike stress concentrations as load magnitude, load direction, and crosstie species are varied. Results from this study indicate that the longitudinal loading, which is not generally present in traditional cut spike fasteners, is more detrimental to the performance of the spike than lateral loading. Further, the depth to the maximum stress concentration increases as the ratio of longitudinal to lateral load increases. Finally, as crosstie species is varied, the magnitude and depth of spike stress changes; these changes are more likely driven by changes in compressive and shear strengths, and then by modulus. Results from this work are presented in an effort to provide information which can be used to mitigate field failures by reducing the spike stresses in an effort to increase the overall safety of HAL freight rail networks and increase the life cycle of premium spike fastening systems.